PROJECT SUMMARY The scientific emphasis of this proposal is to determine the mechanisms of metastatic organotropism observed in pancreatic ductal adenocarcinoma (PDAC) using novel mouse models and functional in vitro assays. It is generally accepted that PDAC develops through a series of premalignant ductal lesions termed pancreatic intraepithelial neoplasia (PanIN). Concurrent with these morphological changes, the epithelium sustains genetic alterations that lead to malignant transformation. Recent work has demonstrated that epithelial-to- mesenchymal transition (EMT) occurs early in the tumorigenesis cascade, causing the tumor cell to lose its epithelial cell identity and begin a plastic transition towards a mesenchymal phenotype that is primed for dissemination and metastasis. It is ultimately this metastasis that leads to death for many PDAC patients and this project will elucidate the molecular mechanisms driving metastasis in this disease. Using genetically engineered mouse models of PDAC, we have identified loss of p120ctn as a catastrophic event that shifts PDAC metastasis from the liver to the lung, a process termed metastatic organotropism. RNA-seq analysis revealed that tumors cells that lose p120ctn dramatically up-regulate parathyroid hormone like hormone (Pthlh), which could potentially explain the metastatic switch from liver to lung. Thus, the overarching hypothesis of this proposal is that p120ctn loss in pancreatic cancer drives EMT and metastasis through upregulation of Pthlh. This hypothesis will be tested by two interrelated specific aims: (1) To determine if Pthlh is necessary to drive EMT and lung metastasis in p120ctn-null cells and (2) To evaluate PTHLH inhibition as a means to block metastasis and define the downstream mechanisms leading to enhanced metastasis by PTHLH. From a clinical standpoint, the site of metastasis is of great import, with patients who have lung-only metastases surviving significantly longer than those who have liver-only or lung and liver metastases. This project will critically address the functional roles of PTHLH in PDAC metastatic organotropism and provide proof-of-principle for anti-PTHLH therapy to inhibit metastatic spread.